FIG. 13 shows a conventional revolution-speed controlling apparatus for a wheel type hydraulic shovel.
In FIG. 13, discharge oil from a hydraulic pump 1 which is driven by an engine (prime mover) 21 is conducted through a hydraulic pilot type of control valve 2 to a hydraulic motor 4 for vehicle propulsion. The changeover operation of the control valve 2 is controlled by a pilot hydraulic circuit comprising a hydraulic pump 5, a pilot valve 6, a slow return valve 7 and a forward/reverse changeover valve 8.
The revolution speed of the engine 21 is controlled by a governor 21a connected through a link mechanism 22 to a fuel lever 23. Upon manipulation of the fuel lever 23, the revolution speed of the engine 21 is adjustable to a desired value in accordance with the manipulation amount of the fuel lever. The governor 21a is also connected through a link mechanism 24 to a vehicle-propelling pedal 6a. Upon an step-on operation of the pedal 6a, simultaneously with the changeover control of the control valve 2, the revolution speed of the engine 21 can be also controlled in accordance with the operation amount of the pedal 6a.
Upon the step-on operation of the vehicle-propelling pedal 6a while the forward/reverse changeover valve 8 is switched to its F-position (forward propulsion position) or R-position (reverse propulsion position), the discharge pressure of the hydraulic pump 5 is controlled by the pilot valve 6, and the pressure which is dependent on the operation amount of the pedal 6a is conducted through the slow return valve 7 and the forward/reverse changeover valve 8 to a control port 2a or 2b of the control valve 2. At this time, the control valve 2 is changed over in a predetermined direction by a predetermined amount, and only an amount of discharge oil corresponding to the changeover amount of the control valve 2 which is a part of the discharge oil of the hydraulic pump 1 rotating in accordance with the operation amount of the vehicle-propelling pedal 6a is conducted to the hydraulic motor 4. Through this operation, the hydraulic motor 4 is driven, and a vehicle is forwardly or reversely propelled at a speed corresponding to the operation amount of the vehicle-propelling pedal 6a.
The discharge oil from the hydraulic pump 1 as described above is also conducted through a control valve 51 to a working cylinder for work (working actuator) 52. The control valve 51 is operated by a working lever 51a to allow the cylinder 52 to be stretched and contracted, whereby a working attachment as not shown is driven to perform a work. If the forward/reverse changeover valve 8 is switched to a neutral position (N-position) at a working time, the control of the engine revolution speed as described above can be performed through the operation of the vehicle-propelling pedal, and thus a finer control (finer adjustment) can be performed than that when the revolution speed control is carried out using the fuel lever 23. Therefore, the engine revolution speed is not required to be undesirably increased, and prevention of noise and improvement in fuel consumption can be performed.
In this kind of construction machine, it is generally required to use the engine at a higher revolution speed range in a vehicle-propelling operation than in a working operation, and in addition the rapid rise-up of the engine revolution speed in response to the operation of the vehicle-propelling pedal 6a is required. However, in the conventional apparatus has a disadvantage that when the engine output is controlled by the vehicle-propelling pedal 6a, the highest revolution speed (maximum output) and the revolution-speed characteristic of the engine 21 can not be altered in both of the vehicle-propelling operation and the working operation. That is, when the engine revolution speed characteristic is beforehand fixedly set to a characteristic which is suitable for the working operation for example, the acceleration of the engine in the vehicle-propelling operation is deteriorated, and conversely when the engine revolution speed characteristic is beforehand fixedly set to a characteristic which is suitable for the vehicle-propelling operation, the operation performance in the working operation is deteriorated, and in addition the fuel consumption and the noise rise up.
An object of this invention is to provide an apparatus for controlling the revolution speed of a prime mover for a hydraulically propelled vehicle in which the revolution speed characteristic of the prime mover can be altered in both vehicle-propelling operation and working operation.
A diesel engine control apparatus in which an engine torque characteristic is altered in accordance with the vehicle propulsion and the work is disclosed in Japanese Laid-open Patent Application No. 62-233430. This apparatus is equipped with two kinds of maximum injection amount characteristics for the engine revolution speed which are provided for the vehicle propulsion and the work, respectively. However, the revolution speed characteristic for the step-on amount of the vehicle-propelling pedal (for example, the rise-up characteristic of the revolution speed for the step-on amount of the vehicle-propelling pedal) is not set selectively in accordance with the vehicle propulsion and the work. Therefore, it is unlikely that all the problems as described above are solved.